This invention relates to a punching machine, and particularly to a toggle punching machine that can keep a sliding block of the punching machine always horizontal when moving up and down.
A punching machine usually depends on rotation of a crankshaft to drive a connecting rod that causes a sliding block to move up while being kept horizontal, in order to down and punch a working piece with a die. It is preferred that the prior punching machine move at a relatively high speed when approaching a working piece in order to shorten time for doing work. However, the speed of the prior toggle punching machine is limited because it must slow its speed down when approaching a working piece causing a relatively longer time for doing work. Therefore, a two-point single toggle mechanism has been proposed as shown in FIG. 1, which is composed of a double eccentric crank shaft with a connecting rod pivot-jointed, i.e., pivotally joined, to each of two opposite positions, the other end of the connecting rods being pivot-jointed pivotally joined to a single toggle mechanism. As FIG. 1 indicates, those two connecting rods driven directly by the crank shaft cannot move linearly, so that the motion angles at the left and right side of the single toggle mechanism are not equal, causing a declined angle (.theta.) during movement of the sliding block under the single toggle mechanism, resulting in a degraded punching quality.
Another two-point single toggle mechanism shown in FIG. 2 is almost the same as shown in FIG. 1 except an approximate rectilinear motion mechanism is added and disposed at the joint of the toggle mechanism and the connecting rods. Though the abovesaid declined angle (.theta.) has been improved more or less, it still fails to hold the sliding block horizontal when moving up and down, and the drawback cannot thus be eliminated for high precision processing.
In view of above imperfection, this invention adopts a single eccentric crankshaft connected with a connecting rod and a guide pin, is pivot-jointed to one set of a double toggle mechanism on the left and right side respectively, and thereby, the sliding block can be always be held horizontal when it moves vertically.